The present invention relates to the transportation of persons in elevator cars and, in particular, to a method and a system for compensating vibrations in elevator cars.
Systems for the transportation of persons often comprise an elevator car that is guided by guide shoes along guide rails. With this type of guidance, vibrations occur which have their origin in the shape and fastening of the guide rails, and/or in pressure variations in the airstream of the elevator car. Such vibrations transferred to the elevator car, especially at high transportation speeds, are unpleasant experiences for the passengers. It is also possible for resonances to occur if the frequency of vibration takes on high values when approaching the resonant frequency of the elevator car.
The U.S. Pat. No. 5,811,743 shows a controlling means for elevator cars in which vibrations are continuously detected by sensors and then compensated by suitable means in a feedback control system. Such compensation of vibrations takes place either by movement of the elevator car relative to the guide shoes, or else by movement of a compensating mass relative to the elevator car. In the latter embodiment, the coupling of the elevator car to the guide shoes is not rigid, but elastic, so that during travel of the elevator car there is a delay in the transfer of vibrations from the guide shoes to the elevator car, and the controlling means has sufficient time to move the compensating mass. By this means vibrations are reduced, but they are not completely eliminated.
The objective of the present invention is therefore to obtain such highly effective compensation of vibrations in systems for transporting persons, that the vibrations are not noticed by the passengers. In particular, vibrations of low frequency are to be compensated, which are known as nuisance vibrations and experienced as particularly annoying by passengers. The apparatus according to the present invention shall be compatible with common technologies and methods of the freight and passenger transportation industry. Furthermore, it should be possible by simple manner and means to retrofit existing passenger transportation systems with the invention.
The present invention is based upon abandonment of the method of compensation of vibrations on elevator cars utilized in the prior art. The basic idea of the present invention consists of detecting vibrations, and especially nuisance vibrations, as early as possible so as to compensate them optimally. This is done by multiple detection of the vibration pattern over time. The vibrations are not only detected at the place where they are experienced as annoying, i.e. on the elevator car, but are also detected where they are generated, i.e. at a source of disturbance.
Thus, the pattern over time of disturbing values of acceleration of the elevator car is detected by at least one acceleration sensor on the elevator car, and the pattern over time of disturbing values of acceleration and/or pressure values is detected by at least one further acceleration and/or pressure sensor at the source of disturbance. Disturbing values of acceleration are caused by, for example, deviations from the perpendicular, and/or ideal line, of a guide shoe along guide rails. Disturbing pressure values are, for example, pressure variations in the airstream of the elevator car. It is advantageous for the acceleration sensor to be attached to a guide shoe, and the pressure sensor attached to the elevator car.
The acceleration values of the elevator car are applied as feedback values, and the acceleration and/or pressure values are applied as disturbance variables to the input of a controlling means. This makes available on the input of the controlling means the pattern over time of disturbance variables and the pattern over time of feedback values, i.e. the effect of the disturbance on the elevator car. The pattern over time of the feedback values, and that of the disturbance variables, is detected as a time function, preferably at regular time intervals. Within this detection accuracy, the time of occurrence of a disturbing force, and its development over time, are detected both at the source of disturbance and on the elevator car.
The relationship between these time functions is described by a transfer function. Disturbance variables and feedback values are interpreted in the controlling means according to the transfer function. The transfer function is based on mechanical parameters of the passenger transportation system, such as the unladen weight of the elevator car, the hardness of the springing/damping elements, the momentary position and the weight of a compensating mass, the momentary load being transported, the momentary distribution of the load in the elevator car, etc. At least one of these mechanical parameters is known, or else its latest value is determined at preferably regular time intervals so its latest value is known. Certain mechanical parameters such as the unladen weight of the elevator car, the weight of the compensating mass, the hardness of the springing/damping elements, can be determined once before the passenger transportation system is put into operation. Other mechanical parameters, such as the position of the compensating mass, the load being transported, and the distribution of the load in the elevator car, can be determined with their latest values.
In the controlling means, disturbance variables are used for feedforward control, and feedback values for feedback control. The transfer function thus allows systematic activation of at least one compensating mass taking into account the known, or latest known, mechanical parameters of the passenger transportation system. Systematic activation of the compensating mass is understood as a driving of the linearly or rotationally moved compensating mass fastened to the elevator car, with the objective of counteracting the disturbing force which has arisen with a compensating force such that the disturbing force is largely neutralized. The disturbing force is neutralized by a compensating force of opposite sign and preferably equal amount. The compensating force need not necessarily be equal in amount to the disturbing force, but it should be at least so large that the vibrations caused by the uncompensated parts of the disturbing force are not perceived by passengers. On the elevator car, the disturbing force as it develops over time is counteracted by a compensating force which develops over time. The compensating mass is moved by at least one drive. The drive is controlled by the controlling means by means of correcting variables.
As well as the compensation of disturbance variables as described, the acceleration of the elevator car is also controlled by feedback. A controlling function for this purpose is provided in the controlling means. For the reference value of acceleration it is given the value zero, since for optimal ride comfort the acceleration on the elevator car should be as low as possible. The feedback value for this feedback control is a measurement value for acceleration detected by at least one sensor. The correcting variable of the control function, and the compensating force compensating the disturbance, together form the correcting variable of the controlling means. Within the freely selectable detection accuracy of the disturbance variables and feedback values, activation of the compensating mass takes place very rapidly, preferably in real time; no time delay in the compensation of vibrations occurs which is perceptible by the passenger, and elimination of the vibrations is total.
In support of this process, low-frequency vibrations of from 1 to 100 Hz, preferably of from 2 to 20 Hz, are systematically isolated by the controlling means. By means of systematically low-frequency correcting variables, the compensating mass is driven with correspondingly low frequency, and nuisance vibrations systematically eliminated.